Synthesis and characterization of rigid +2 and +3 heteroleptic dinuclear ruthenium(II) complexes (original) (raw)
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Indian Journal of …, 2011
Synthesis and characterisation of the ruthenium complexes, [Ru II (Q)(tppz)(Cl)]ClO 4 (1) and [{Ru II (Q)Cl} 2 -(µ-tppz)](ClO 4 ) 2 (2), incorporating redox noninnocent ligands, (Q = o-benzoquinonediimine, tppz = 2,3,5,6-tetrakis-(2-pyridyl)pyrazine) are reported. The crystal structure of (1) and DFT optimized structure of (2) in comparison with the reported structures of analogous molecules establish that their valence configurations comprise the fully oxidized Q o and tppz o along with the Ru(II) center as well as non-planarity of the coordinated tppz. The reversible Ru II /Ru III oxidation of (1) and two successive Ru II /Ru III couples for (2) appear at 0.95 V and 0.96, 1.11 V vs SCE in CH 3 CN, respectively. The separation in potential of 0.15 V between the two successive oxidation processes in (2) leads to the comproportionation constant, K c value of 3.5×10 2 , which implies a rather weakly coupled (electrochemical) valence localized class II mixed valent Ru II Ru III state in (2) + . However, the DFT calculated Mulliken spin densities of (2) + (Ru1, Ru2, Q, tppz and Cl of 0.333, 0.412, 0.070, −0.006 and 0.221, respectively) suggest an almost valence averaged situation. The compositions of molecular orbitals of (1) and (2) suggest appreciable (dπ)Ru II →π * (tppz)/π * (Q) back-bonding. Both the complexes exhibit multiple close-by reductions within the potential range of 0 to −2.0 V vs SCE in CH 3 CN which are assigned to be the ligand (Q/tppz) based reductions. The molecular orbital compositions predict Q based first reduction followed by tppz-based successive reductions in (1), whereas in (2) first reduction primarily takes place at the bridging tppz center followed by the reduction of Q. (1) and (2) exhibit multiple metal-to-ligand charge transfer transitions in the visible region due to the presence of two and three acceptor ligands, respectively. The key transitions in the visible region are assigned based on the TD-DFT calculations on optimized structures of (1) and .
1997
We have prepared the mononuclear complexes [Ru(bpy) 2 (AB)][PF 6 ] 2 , [Ru(bpy)(AB) 2 ][PF 6 ] 2 , and [Ru(AB) 3 ][PF 6 ] 2 (designated Ru-AB, Ru-AB 2 , and Ru-AB 3 , respectively) [where bpy is 2,2′-bipyridine and AB is the asymmetric bis(bipyridyl) bridging ligand 2,2′:3′,2′′:6′′,2′′′-quaterpyridine] in which there are one, two, or three (respectively) bpy-type fragments pendant from the {Ru(bpy) 3 } 2+ core. In every case the less hindered site A of the ligand AB is coordinated to Ru(II) and the more hindered site B is pendant. Reaction with Re(CO) 5 Cl affords the heteronuclear complexes [Ru(bpy) 2 {ABRe(CO) 3 Cl}][PF 6 ] 2 , [Ru(bpy){ABRe(CO) 3 Cl} 2 ][PF 6 ] 2 , and [Ru{ABRe(CO) 3 Cl} 3 ][PF 6 ] 2 (designated Ru-ABRe, Ru-ABRe 2 , and Ru-ABRe 3 , respectively) in which each pendant site B is now coordinated to a {Re(CO) 3 Cl} fragment. Because of the conformational properties of the AB ligand, in the tetranuclear Ru-ABRe 3 complex the Ru-based chromophore occupies an internal position in a sort of molecular ball, the three Re-based groups being located outside. Electrochemical studies show that the pendant {Re(CO) 3 Cl} fragments exert an electron-withdrawing effect on the {Ru(bpy) 3 } 2+ core such that the Ru(II)/Ru(III) redox couple moves to more positive potentials as the number of pendant {Re(CO) 3 Cl} fragments increases. We employed steady-state and time-resolved luminescence spectroscopy to investigate the Re f Ru intercomponent energy transfer taking place in the mixed-metal complexes and found that Re f Ru energy transfer takes place with 100% efficiency in all cases. For the tetranuclear complex, it is thus possible to convey a substantial portion of the electronic excitation energy from the molecular periphery to the center. It is also found that the peripheral Re-containing units exert a shielding effect against luminescence quenching processes at the Ru center by molecular oxygen dissolved in the solvent. During the syntheses, the unexpected byproduct [Ru(AB)(η 3 -AB)Cl][PF 6 ] was also isolated in which one of the AB ligands is coordinated in a hitherto unseen terdentate mode; this was crystallographically characterized. Data for [Ru(AB)(η 3 -AB)Cl][PF 6 ]‚2MeCN: C 44 H 34 ClF 6 N 10 PRu; triclinic, P1 h; a ) 10.578(3) Å, b ) 14.330(2) Å, c ) 14.761(3) Å; R ) 84.56(2)°, ) 70.408(12)°, γ ) 86.03(2)°; V ) 2096.8(8) Å 3 ; Z ) 2.
Polyhedron, 2010
The reaction of RuX 3 (X = F, CI, Br) with arylazoimine (PhN@NC(COCH 3 )@NPh, Az) and (4,4 0 -di-tert-butyl-2,2-bipyridine, dtb) in refluxing ethanol affords a trans-[Ru(Az)(dtb)X 2 ]. These complexes have been characterized through spectroscopic (IR, UV/Vis, and NMR) and electrochemical (CV) techniques. The complex trans-[Ru(Az)(dtb)Cl 2 ] has been X-ray crystallographically characterized. The crystals belong to the rhombohedral space group R 3. The two chlorine atoms are trans to each other. The 4,4 0 -di-tert-butyl-2,2-bipyridine ligand is bent and the Az ligand rings are rotated, due to inter-ligands steric interactions between H atoms of opposite pyridyl units across the Ru center. These complexes display a cyclic voltammetric oneelectron metal oxidation peak in acetonitrile near 1.2 V versus NHE. The electronic absorption spectra of these complexes show a strong band in the visible region which is assigned to a (Ru(II)-to-azomethine) MLCT transition based on TD-DFT calculations.
Inorganic Chemistry, 1996
The first luminescent and redox active multinuclear Ru(II) compound containing both electron-poor (2,3-bis(2pyridyl)pyrazine, 2,3-dpp) and electron-rich (3,5-bis(pyridyn-2-yl)-1,2,4-triazole, Hbpt) polypyridine bridging ligands has been synthesized. The novel compound is [(bpy) 2 Ru(µ-bpt)Ru{(µ-2,3-dpp)Ru(bpy) 2 } 2 ] 7+ (1; bpy ) 2,2′-bipyridine). Its absorption spectrum, luminescence properties, and redox behavior have been studied and are compared with the properties of the parent complexes [Ru{(µ-2,3-dpp)Ru(bpy) 2 } 3 ] 8+ (2) and [(bpy) 2 Ru(µbpt)Ru(bpy) 2 ] 3+ (3). The absorption spectrum of 1 is dominated by ligand-centered bands in the UV region and by metal-to-ligand charge transfer bands in the visible region. Excited states and oxidation and reduction processes are localized in specific sites of the multicomponent structure. However, perturbations of each component on the redox and excited states of the others, as well as electronic interactions between the chromophores, can be observed. Intercomponent energy transfer from the upper-lying (µ-bpt)(bpy)Rufbpy CT excited state of the Ru(bpy) 2 (µbpt) + component to the lower-lying (bpy) 2 Rufµ-2,3-dpp CT excited state of the Ru(bpy) 2 (µ-2,3-dpp) 2+ subunit(s) is efficient in 1 in fluid solution at room temperature, whereas this process is not observed in a rigid matrix at 77 K. A two-step energy transfer mechanism is proposed to explain the photophysical properties of the new compound. X Campagna, S.; Juris, A.; Ciano, M.; Balzani, V. In PerspectiVes in Coordination Chemistry; Williams, A. F.; Floriani, C.; Merbach, A. E., Eds.; VCH: Basel, 1992, p 153. (f) Amadelli, R.; Argazzi, R.; Bignozzi, C. A.; Scandola, F. Frank, M.; Nieger, M.; Belser, P.; von Zelewsky, A.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L. Angew. Chem., Int. Ed. Engl. 1993, 32, 1643. (i) Barigelletti, F.; Flamigni, L.; Balzani, V.; Collin, J.-P.; Sauvage, J.-P.; Sour, A.; Constable, E. C.; Cargill Thompson, A. M. W.
Polyhedron, 2013
Five trans-[Ru(P-P) 2 Cl 2 ] complexes were prepared by reacting RuCl 2 (PPh 3 ) 3 with P-P ligands {P-P = 3-hexyl-1,3-bis(diphenylphosphino)propane (hdppp) (1); = 1,3-bis(diphenylphosphino)propane (dppp) (2); = 1,2-bis(diphenylphosphino)ethane (dppe) (3); 1.1 0 -bis(diphenylphosphino)methane (dppm) (4); 1,2-bis(diphenylphosphino)ethylene (depe) (5)}. The complexes were characterized by an elemental analysis, IR, 1 H, 13 C and 31 P{1H}NMR, FAB-MS and TG/DTA. These Ru(II) complexes showed Ru(III)/Ru(II) quasireversible redox couple. The molecular structures of the complexes 1 and 3 were determined by X-ray crystallography, and their spectroscopic properties were studied. Another polymorph of 3 was reported in literature, the reported polymorph of 3 in this work crystallizes in P 1 space group, whereas, the previously reported polymorph crystallizes in C2/c space group. The two complexes adopt a distorted trans octahedral coordination and ruthenium(II) ions are located on a crystallographic centre of symmetry. Based on the optimized structures, computational investigations were carried out in order to determine the electronic structures of the complexes. The electronic spectra of 1 and 1 + in dichloromethane were calculated with the use of time-dependent DFT methods, and the electronic spectra of the transitions were correlated with the molecular orbitals of the complexes.
Electronic structures of ruthenium complexes encircling non-innocent ligand assembly
Journal of Chemical Sciences, 2012
Electronic structural forms of selected mononuclear and dinuclear ruthenium complexes encompassing redox non-innocent terminal as well as bridging ligands have been addressed. The sensitive valence and spin situations of the complexes have been established in the native and accessible redox states via detailed analysis of their crystal structures, electrochemistry, UV/VIS/NIR spectroelectrochemistry, EPR signatures at the paramagnetic states and DFT calculations. Mononuclear complexes exhibit significant variations in valence and spin distribution processes based on the simple modification of the non-innocent ligand frameworks as well as electronic nature of the co-ligands, σ-donating or π-accepting. Dinuclear complexes with modified pyrazine, p-quinone and azo-derived redox-active bridging ligands show complex features including redoxinduced electron-transfer (RIET), remote metal to metal spin-interaction in a three-spin metal-bridge-metal arrangement as well as electron-transfer driven chemical transformation (EC).
The Journal of Physical Chemistry, 1996
The PF 6salts of the dinuclear complexes [(bpy) 2 Ru(PAP)Ru(bpy) 2 ] 4+ (Ru II PAPRu II ), [(bpy) 2 Os(PAP)Os-(bpy) 2 ] 4+ (Os II PAPOs II ), and [(bpy) 2 Ru(PAP)Os(bpy) 2 ] 4+ (Ru II PAPOs II ) have been prepared, where bpy ) 2,2′-bipyridine and PAP is a rodlike bridging ligand made of an adamantane-based spacer collinear with the coordination axis of two 1,10-phenanthroline units. In the prepared complexes, the metal-metal distance is 2.1 nm. In the Ru II PAPOs II compound, photoinduced energy transfer from the Ru II -based to the Os II -based unit takes place with rate constant 5.2 × 10 7 s -1 at room temperature and 2.4 × 10 7 s -1 at 77 K. In the mixed-valence Ru II PAPOs III compound, the luminescent excited state of the Ru II -based unit is quenched via electron transfer by the Os III -based unit with rate constant 7.2 × 10 6 s -1 . The rate constant for the backelectron-transfer reaction is 8.3 × 10 3 s -1 .
Dalton Transactions, 2007
Structurally characterised 2,5-bis(2-hydroxyphenyl)pyrazine (H 2 L) can be partially or fully deprotonated to form the complexes [(acac) 2 Ru(l-L)Ru(acac) 2 ], [1], acac − = acetylacetonato = 2,4-pentanedionato, [(pap) 2 Ru(l-L)Ru(pap) 2 ](ClO 4) 2 , [2](ClO 4) 2 , pap = 2-phenylazopyridine, or [(pap) 2 Ru(HL)](ClO 4), [3](ClO 4). Several reversible oxidation and reduction processes were observed in each case and were analysed with respect to oxidation state alternatives through EPR and UV-VIS-NIR spectroelectrochemistry. In relation to previously reported compounds with 2,2-bipyridine as ancillary ligands the complex redox system [1] n is distinguished by a preference for metal-based electron transfer whereas the systems [2] n and [3] n favour an invariant Ru II state. Accordingly, the paramagnetic forms of [1] n , n = −, 0, +, exhibit metal-centred spin whereas the odd-electron intermediates [2] + , [2] 3+ and [3] show radical-type EPR spectra. A comparison with analogous complexes involving the 3,6-bis(2-oxidophenyl)-1,2,4,5-tetrazine reveals the diminished p acceptor capability of the pyrazine-containing bridge.